In the ITU-R (International Telecommunication Union-Radio Communication Sector), fourth generation mobile communication systems called “IMT-Advanced (International Mobile Telecommunications-Advanced)” are required to support extremely high data rates compared to current third generation mobile communication systems. A reduction of coverage caused by constraints on transmission power in transmission from mobile terminal apparatuses in particular becomes a technical problem in realizing such high data rates.
Relay transmission is becoming a focus of attention in recent years as a technique for realizing high- speed radio transmission with wide coverage in a power-constrained environment. Relay transmission can be roughly divided into an AF (Amplify-and-Forward) type that amplifies without demodulation and transfers a reception RF (Radio Frequency) signal and a DF (Decode-and-Forward) type in which a radio relay station apparatus demodulates/decodes a received signal to be relayed, re-codes/re-modulates the decision data and transfers the data.
The AF type relay transmission has an advantage that a transmission delay time required for relay transfer is small, but a radio relay station apparatus amplifies and transfers noise and an interference component included in a received signal as well as a desired signal component, resulting in a problem that inter-cell interference increases in cellular communication. Furthermore, since relay transmission generally requires part of a communication band to be allocated to a relay signal, frequency utilization efficiency deteriorates.
Thus, the present inventor previously proposed an adaptive AF type relay transmission method that controls whether or not to apply relay transmission in two stages based on the magnitude of path loss between a mobile terminal apparatus and a radio base station apparatus, and between the mobile terminal apparatus and each radio relay station apparatus, and controls which radio relay station apparatus should be used to perform relay transmission (Non-Patent Literature 1, Patent Literature 1).